Readers.getReader, Writers.getWriter API change.

Now these functions return a pair of a reader/writer and an
Extensions, instead of building the extensions into the
reader/writer.  The calling code must explicitly set
readerExtensions or writerExtensions using the Extensions
returned.

The point of the change is to make it possible for the
calling code to determine what extensions are being used.

See #3659.

1 files changed, 4 insertions, 7 deletions

diff --git a/src/Text/Pandoc/Writers.hs b/src/Text/Pandoc/Writers.hs
index dbe55449f..6dfc1a7b3 100644
--- a/src/Text/Pandoc/Writers.hs
+++ b/src/Text/Pandoc/Writers.hs
@@ -176,19 +176,16 @@ writers = [
   ,("muse"         , TextWriter writeMuse)
   ]
 
-getWriter :: PandocMonad m => String -> Either String (Writer m)
+-- | Retrieve writer, extensions based on formatSpec (format+extensions).
+getWriter :: PandocMonad m => String -> Either String (Writer m, Extensions)
 getWriter s
   = case parseFormatSpec s of
          Left e  -> Left $ intercalate "\n" [m | Message m <- errorMessages e]
          Right (writerName, setExts) ->
              case lookup writerName writers of
                      Nothing -> Left $ "Unknown writer: " ++ writerName
-                     Just (TextWriter r) -> Right $ TextWriter $
-                             \o -> r o{ writerExtensions = setExts $
-                                              getDefaultExtensions writerName }
-                     Just (ByteStringWriter r) -> Right $ ByteStringWriter $
-                             \o -> r o{ writerExtensions = setExts $
-                                              getDefaultExtensions writerName }
+                     Just r -> Right (r, setExts $
+                                  getDefaultExtensions writerName)
 
 writeJSON :: WriterOptions -> Pandoc -> Text
 writeJSON _ = UTF8.toText . BL.toStrict . encode